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| articles:nist_traceability [2019/05/25 12:20] – [What are SI Units?] rrandall | articles:nist_traceability [2019/06/12 22:32] – [Conclusion] rrandall |
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| ===== What are SI Units? ===== | ===== What are SI Units? ===== |
| {{ :articles:2018-si.png?direct&130|}} | {{ :articles:2018-si.png?direct&130|}} |
| Adopted by the [[https://en.wikipedia.org/wiki/General_Conference_on_Weights_and_Measures|General Conference on Weights and Measures (CGPM)]] in 1960, the "[[https://www.bipm.org/en/measurement-units/|International System of Units]]" (//Système International d'Unités//, with the international abbreviation SI) consists of 7 base units that define 22 derived units. With the exception of the kilogram, the base SI units are all derived from intrinsic (i.e., invariant) constants of nature, such as the speed of light in vacuum and the [[https://en.wikipedia.org/wiki/Boltzmann_constant|Boltzmann constant]] (which serves as the basis for the Kelvin temperature scale). According to Dr. Chris Sutton, "[[https://www.sciencelearn.org.nz/resources/1872-non-si-units|the SI system of units allows for complete coverage of all scientific measurements]]". \\ | Adopted by the [[https://en.wikipedia.org/wiki/General_Conference_on_Weights_and_Measures|General Conference on Weights and Measures (CGPM)]] in 1960, the "[[https://www.bipm.org/en/measurement-units/|International System of Units]]" (//Système International d'Unités//, with the international abbreviation SI) consists of 7 base units that define 22 derived units. The base SI units are all derived from intrinsic (i.e., invariant) constants of nature, such as the speed of light in vacuum and the [[https://en.wikipedia.org/wiki/Boltzmann_constant|Boltzmann constant]] (which serves as the basis for the Kelvin temperature scale). According to Dr. Chris Sutton, "[[https://www.sciencelearn.org.nz/resources/1872-non-si-units|the SI system of units allows for complete coverage of all scientific measurements]]". \\ |
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| The SI Units are defined in the [[https://www.bipm.org/en/publications/si-brochure/|SI Brochure]], which is published by the [[https://www.bipm.org/en/about-us/|“Bureau International des Poids et Mesures” (BIPM)]], located in France. | The SI Units are defined in the [[https://www.bipm.org/en/publications/si-brochure/|SI Brochure]], which is published by the [[https://www.bipm.org/en/about-us/|“Bureau International des Poids et Mesures” (BIPM)]], located in France. |
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| SI Units are also explained on the NIST web site at: https://www.nist.gov/pml/weights-and-measures/metric-si/si-units | |
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| Alternatively, SI Units are also discussed in "[[https://www.nist.gov/pml/special-publication-330|NIST Special Publication 330 - The International System of Units (SI)]]"; which will likely be updated since a significant update to the SI went into effect on May 20, 2019. The new definitions impact four of the base units: | |
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| * The kilogram – will be defined in terms of the Planck constant (h) | |
| * The ampere – will be defined in terms of the elementary charge (e) | |
| * The kelvin – will be defined in terms of the Boltzmann constant (k) | |
| * The mole – will be defined in terms of the Avogadro constant (NA) | |
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| Because SI units are derived from intrinsic (i.e., invariant) constants of nature, "intrinsic measurement standards" exist. This is acknowledged in ISO 17025:2017, sec. 6.5.2, which provides 3 (three) different methodologies for achieving metrological traceability. And is further clarified in ISO 17025:2017, "Annex A: Metrological traceability". \\ | Because SI units are derived from intrinsic (i.e., invariant) constants of nature, "intrinsic measurement standards" exist. This is acknowledged in ISO 17025:2017, sec. 6.5.2, which provides 3 (three) different methodologies for achieving metrological traceability. And is further clarified in ISO 17025:2017, "Annex A: Metrological traceability". \\ |
| b) a documented unbroken chain of calibrations going back to stated and appropriate references (appropriate references include national or international standards, and __intrinsic standards__);// | b) a documented unbroken chain of calibrations going back to stated and appropriate references (appropriate references include national or international standards, and __intrinsic standards__);// |
| </WRAP> | </WRAP> |
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| | SI Units are also explained on the NIST web site at: https://www.nist.gov/pml/weights-and-measures/metric-si/si-units and in "[[https://www.nist.gov/pml/special-publication-330|NIST Special Publication 330 - The International System of Units (SI)]]". Both NIST sources will likely be updated soon to reflect the new definitions to the SI that went into effect on May 20, 2019. |
| ===== What are "intrinsic" standards? ===== | ===== What are "intrinsic" standards? ===== |
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| </WRAP> | </WRAP> |
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| Unless required by statute or regulation (i.e., for Legal Metrology), mandating "NIST traceability" unnecessarily "limits" the sources for metrological traceability, excluding other NMIs and/or accredited commercial metrology laboratories. | Unless required by statute or regulation (i.e., for [[https://www.oiml.org/en/about/legal-metrology|Legal Metrology]]), mandating "NIST traceability" unnecessarily "limits" the sources for metrological traceability, excluding other NMIs and/or accredited commercial metrology laboratories. |
